Electrolysis of ammonium chloride



Patented July 30, 1940 PATENT OFFICE ELECTROLYSIS OF AMIVIONIUM CHLORIDEVaman R. Kokatnur, Beechhurs t, N. Y., and Oliver S. Plantinga,Montclair, N. J., assignors to Autoxygen Inc., New York, N. Y., acorporation of New York No Drawing. Application May 5, 1987, Serial No.140,890

3 Claims.

This invention relates to the electrolysis of ammonium chloride for therecovery or production of chlorine or ammonia or both.

While ammonium chloride in aqueous solution is easily decomposed byelectrolytic action, the process is not commonly employed on account ofthe great danger from the tendency of ammonia and chlorine to react andform the highly explosive compound nitrogen trichloride. It is also arather expensive raw material to employ for the production of chlorine,under ordinary circumstances, and this fact alone would tend todisqualify it for commercial chlorine production even if the process ofelectrolytic decomposition were not so dangerous. We have found certainconditions under which chlorine or ammonia, or both of these materials,may be electrolytically produced from aqueous solutions of ammoniumchloride, without the formation of the explosive nitrogen trichloride.At the same time, our discovery opens the way to the economical use ofthis material for the electrolytic production of chlorine.

While we have mentioned the formation of nitrogen trichloride by thereaction of chlorine on ammonia, there are other objectionable productswhich would often be formed in the electrolysis of aqueous ammoniumchloride solutions, for example, the mono and dichloramines andnitrogen. Our discovery also makes it possible to avoid the formation ofthese products.

The underlying principle on which the invention is based resides in theelectrolysis of aqueous ammonium chloride solutions in the presence ofchlorides of alkali metal and alkaline earths which we find inhibit theproduction of nitrogen trichloride, and such products as nitrogen andchloramines. Under proper conditions, the electrolyte, containingammonium chloride and one or more chlorides of alkali metal or alkalineearths, can be electrolyzed to produce ammonia and chlorine from theammonium chloride without. substantially reducing the content of theother chlorides. It is, however, important that the other chlorides bepresent in substantial quantities, for example, one-third chemicalequivalent of the ammonium chloride, if the full advantages of theinvention are to be obtained. Preferably, the ratio of the other metalchloride to ammonium chloride, on the basis of chemical equivalents, isat least 1-1, that is to say, the other chloride should at least equaland may even exceed the ammonium chloride in terms of chemicalequivalents. The total concentration of the electrolyte may be, forexample, between 25% and 30% solids. The temperature in the electrolyteshould not be below 35 C., and it should preferably be maintained aroundto 0., although as high as 90 C. is not at all harmful. The anodecurrent density in a 26% aqueous solution of ammonium chloride andsodium chloride, for example, at 65 C., may be maintained at fro'm 100to 150 amperes per square foot, under which conditions, with suitableelectrodes and cell construction, the decomposition etficiency of theammonium chloride may amount to from to of the theoretical, theefllciency approaching the higher figure as the percentage of the sodiumchloride approaches or exceeds that of the ammonium chloride.

It is important in electrolyzing the mixed solu- I tions to have theanode compartment as small as can conveniently be arranged in anelectrolytic cell. Any of the well-known types of electrolytic cells,such asused for the electrolysis of sodium chloride, may be employed,for example, a diaphragm cell, a cell of the bell-jar type, or a mercurycell. If the diaphragm cell is used, asbestos paper is used as thediaphragm. The cathode may be of perforated iron or of any otherconducting material which is inert to sodium and ammonium chlorides aswell as hydroxides. The anode may be of the usual carbon, graphite ormagnetite, composition. If a mercury cell is used, the cathode should bedipped into the mercury and the cathode chamber should be sumcientlylarge to take care of the large volume necessitated by mercury, andammonium amalgam. The voltage required in, for example, the Vorce typeof diaphragm cell about four feet high and two feet in diameter, isbetween 3 and 5 volts, at about 1200 amperes current. This voltage, aswell as the amperage, will vary somewhat, depending upon theconcentration and the temperature of the electrolyte, the resistance andpolarizations. The current density may be kept between, for example, andamperes per square foot of anode surface in a 26% aqueous solutioncontaining chemical equivalents of sodium chloride and ammoniumchloride. The flow of electrolyte may be maintained between, say, 15 and20 liters per hour, and the temperature at about 60 C. The rate of flowwith respect to the. current density should be so adjusted as to keepthe ammonium chloride concentration in the eflluent from the cell as lowas possible.

Under the conditions recited, nearly two parts by weight of chlorine areproduced for each part of ammonia. The. purit'yof the chlorine producedis generally over 96%, and the remaining solution contains very littleammonium chloride. The sodium chloride remains approximately constant,and hence the regeneration of the solution to be returned to the cellmay be principally accomplished by'the addition of ammonium chloride,although some addition of sodium chloride may be required to keep thecomposition of the electrolyte entering the cell in cyclic operationapproximately constant.

Instead of passing a mixed solution of ammonium chloride and sodiumchloride through the cell, the two solutions of ammonium chloride andsodium chloride respectively, at about 25% concentration, may beseparately passed through the anode and cathode compartments, that is tosay, the solution of ammonium chloride may be passed through the anodecompartment and the solution of sodium chloride through the cathodecompartment. The operating conditions may in other respects be similarto those employed when the mixed solution is used.

The electrolysis of the mixed solution of sodium chloride and ammoniumchloride is especially advantageous when introduced as a step in theammonia soda process. In the ammonia soda process, the ammonium chlorideliquor, from which the ammonia is to be recovered for use again in theproduction of sodium bicarbonate, contains substantial quantities ofsodium chloride. The composition of this liquor commonly runs from 1'?to 18% ammonium chloride, and '7 to 8% sodium chloride. By employing theprocess of our present invention in the ammonia soda process, theammonia is returned to the system for reaction with carbon dioxide andsodium chloride, and the chlorine is recovered as a valuable by-product,where heretofore the chlorine has been discharged from the systemusually in the form of calcium chloride, for which there is no largemarket. The economy of the process of this invention is, therefore,particularly marked when the process is employed in conjunction with theproduction of. soda by the ammonia soda process. The invention may thusbe regarded as offering an improvement in the ammonia soda process. Theelectrolyte coming from the decomposition cell has been largely depletedof its ammonium chloride content, and to a much less extent of itssodium chloride. Since the liquor from the ammonia soda process is muchhigher in ammonium chloride than in sodium chloride, the regeneration ofthe spent electrolyte by the addition of suitable quantities of theliquor from the ammonia soda process ofiers an economical method for thecontinuous electrolytic production of chlorine from ammonium chloridewithout the danger of forming nitrogen trichloride and substitutionproducts thereof, while at the same time restoring to the soda processthe ammonia which heretofore has usually been recovered at the expenseof converting the chlorine into the relatively much cheaper by-product,calcium chloride.

We claim:

1. The method of producing substantially pure chlorine and recoveringammonia in good yield from aqueous ammonium chloride solutions, whichcomprises passing an electrolyzing current through an electrolytic cellhaving an aqueous electrolyte containing ammonium and sodium chlorides,the concentration of the sodium chloride being at least equal to that ofthe ammonium chloride, thereby discharging the am monium ions from thecatholyte containing chlorides of ammonium and sodium and dischargingchlorine ions from the anolyte containing sodium chloride and anyresidual ammonium chloride.

2. The method of producing substantially pure chlorine and recoveringammonia in good yield from aqueous ammonium chloride solutions, whichcomprises passing an electrolyzing current through an electrolytic cellhaving an aqueous electrolyte containing ammonium chloride and achloride selected from the group consisting of alkali metal chloridesand alkaline earth metal chlorides at a concentration at least one thirdof an equivalent of the ammonium chloride, thereby discharging ammoniumions from the catholyte containing chloride of ammonium and the chlorideselected from the group consisting of alkali metal chlorides andalkaline earth metal chlorides, and discharging chlorine from theanolyte containing the chloride selected from the group consisting ofalkali metal chlorides and while maintaining the temperature in theneighborhood of 60 to 65 0., thereby discharging ammonium ions from thecatholyte containing chloride of ammonium and the chloride selected fromthe group consisting of alkali metal chlorides and alkaline earth metalchlorides, and discharging chlorine from the anolyte containing thechloride selected from the group consisting of alkali metal chloridesand alkaline earth metal chlorides and any residual ammonium chloride.

VAMAN R. KOKATNUR.

OLIVER S. PLANTINGA.

